Lecture #22: Endocrine System--Posterior Puitary, Thyroid, and Parathyroid

Question 1

What is the function of the posterior pituitary gland?

Answer 1

• Does not synthesize hormones

• Consists of axon terminals from two groups of hypothalamic
neurons

• These neurons release two peptide hormones that enter
capillaries
– Antidiuretic Hormone (ADH) or vasopressin
– Oxytocin (OT)

Question 2

What types of neural tissues is in the posterior pituitary gland?

Answer 2

resembles neural tissue with glial cells,

nerve fibers, nerve endings, and neurosecretory vesicles.

Question 3

Where is ADH and OT transpoted after they are made in the hypothalamus?

Answer 3

are transported into the neurosecretory
vesicles where they are stored until a signal comes to
stimulate release.

Question 4

What is Anti-duretic hormone (ADH)?

Answer 4

ADH produced by cells in supraoptic nucleus in the
hypothalamus in response to signals from
osmoreceptors (hydration status)

Question 5

What are the actions of ADH?

Answer 5

– Prevents diuresis – decreases urine production by stimulating
the kidneys to return more water back to the blood

– Prevents water loss in sweat glands

– Causes constriction of arterioles (Vasopressin)

Question 6

What is the regulation of ADH?

Answer 6

Dehydration or high osmolarity of
blood
– ADH released from posterior
pituitary

• Overhydration or low osmolarity
of blood
– ADH release inhibited

• ADH release inhibited by alcohol

• Lack of ADH results in diabetes
insipidus
– Inability of the kidneys to conserve H2O
– Excessive urination

Question 7

What is oxytocin? (OT)

Answer 7

Produced by cells in
the paraventricular
nucleus of the
hypothalamus

Question 8

What is Oxytocin target cells?

Answer 8

• Two target tissues:
– Uterus: during labor
– Mammary glands:
after delivery

Question 9

What is the regulation of oxytoncin during labor?

Answer 9

• Stimulation of uterus by baby’s head
causes stretch of cervix

• Oxytocin release from posterior pituitary
• Uterine smooth muscle contracts

• As the baby’s head is pushed into the
cervix, oxytocin release increases

• muscle contraction, which pushes the
baby further and elicits even more
oxytocin release

• When baby is born, the positive feedback
loop ceases.

Question 10

How does oxytoxcin effect mammary glands?

Answer 10

• Effect on Mammary Glands
– suckling & hearing baby’s cry stimulates oxytocin release
– oxytocin causes muscle contraction & milk ejection

• Lactation is the process of milk production and ejection
– milk production is stimulated by Prolactin
– Prolactin and Oxytocin work together in lactation

Question 11

How do thyroid hormones form?

Answer 11

• Iodide trapping by follicular cells
• Synthesis of thyroglobulin (TGB)
• Release of TGB into colloid
• Iodination of tyrosine in colloid

• Formation of T3 & T4 by combining T1
and T2
together

• Uptake & digestion of TGB by follicle
cells

• Secretion of T3 & T4
into blood; binds
to thyroxine binding globulin (TBG)

Question 12

What is the function of thyroid hormones?

Answer 12

• Increase basal metabolic rate by stimulating the cellular use
of O2
to produce ATP –> increased cellular catabolism of
glucose (glycolysis), fatty acids (beta oxidation) and
triglycerides (lipolysis)

• Increase synthesis of Na+
/K+ ATPase –> more ATP is used to
pump ions –> ATP use produces heat, which raises body
temperature –> called the calorigenic effect

• Enhance some actions of sympathetic nervous system by upregulating
beta-receptors –> increased heart rate,
contractility and blood pressure

• Stimulate growth (in conjunction with hGH and insulin)
particularly during development

Question 13

What is Hyposecretion?

Answer 13

• During development, infancy and/or early childhood results in dwarfism and severe mental retardation (congenital
hypothyroidism or cretinism)

• In the adult results in edema, low heart rate, muscle
weakness, sensitivity to cold, low body temperature, weight
gain and mental dullness (myxedema)

Question 14

What is Hypersecretion?

Answer 14

Hyperthyroidism
(Graves’ disease)
– weight loss, nervousness,
tremor, increased heart
rate and blood pressure ,
exophthalmos (edema
behind eyes), high body
temp, sweating

Question 15

What is Goiter?

Answer 15

• enlarged thyroid (usually due to dietary
lack of iodine)

• occurs because TSH levels are high –> stimulates growth of thyroid gland

• can be associated with hyperthyroidism,
hypothyroidism or euthyroidism

• dietary lack of iodine leads to lowthyroid hormone (T3/T4) production –> stimulates TSH by negative feedback –>stimulates thyroid gland growth

Question 16

What cell does calcitonin associate with?

Answer 16

secreted by parafollicular (C) cells of the thyroid gland. Lowers blood Ca2+ levels by
inhibiting osteoclasts

Question 17

What is a parathyroid hormone?

Answer 17

secreted by chief cells of
the parathyroid gland.
Raises blood Ca2+ levels
by stimulating osteoclasts

Question 18

What are the primary functions of the Parathyroid hormone?

Answer 18

• Raises blood calcium levels
• increases activity of osteoclasts
• increases reabsorption of Ca2+ by kidney
• inhibits reabsorption of phosphate (HPO4)2-
• promotes formation of calcitriol (active vitamin D) by kidney which increases absorption of Ca2+ and Mg2+ by intestinal tract

Question 19

Draw or describe the cycle of the parathyroid hormone with the associate of Calcium levels.

Answer 19

1. High level Ca2+ in blood stimulates thyroid gland parafollicular cells to release more CT
2. Calcitonin inhibits osteoclasts, thus decreasing blood Ca2+ level
3. Low Level Ca2+ in blood stimulates parathyroid gland chief cells to release more PTH
4. Parathyroid hormone (PTH) promotes resorption of Ca2+ from bone extracellular matrix into blood extracellular matrix into blood and retards loss of Ca2+ in urine, thus increasing blood Ca2+ level
5. PTH also stimulates the kidneys to release calcitriol
6. Calcitriol stimulates increased absorption of Ca2+ from foods, which increases blood Ca2+ level